This invention is related to a valve arrangement of the type comprised of a housing in which an electromagnetically actuatable preliminary control valve for controlling a differential pressure and a main valve actuatable by the differential pressure are arranged and whose closing element provides for selectively connecting an outlet connection with at least one inlet connection.
A valve arrangement of this kind is illustrated, for example, in a publication of Messrs. MAC Valves Europe Inc. That arrangement is provided with an electromagnetically actuatable preliminary control valve with the aid of which the supply of a pressurized pressure fluid, such as compressed air, to a piston of a main valve is controlled. The piston in this device is guided in a sealed manner within a bore and presents two sealing edges which by interaction with two sealing seats either establish or shut off a connection between a first, a second and a third connection, respectively.
In this known valve arrangement, it is a significant disadvantage to have to provide a compressed air source which makes the valve arrangement less suited for use in automotive vehicles in which there is no readily available compressed air source but rather only a vacuum source.
The relatively long change-over times of this prior art valve arrangement which are due to the friction caused during the motion of the heavy piston is also regarded as a shortcoming.